1. Field of the Invention
The present invention relates to optical communication equipment and, more specifically, to signal processing in optical receivers of on-off keying (OOK) and/or pulse amplitude modulation (PAM) signals.
2. Description of the Related Art
This section introduces aspects that may help facilitate a better understanding of the inventions. Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art.
A polarization-diverse intradyne receiver operates on an optical signal having two independently modulated polarization components. The receiver may employ sophisticated signal processing to recover the two corresponding data streams. However, there are two major challenges that hinder the advancement of this technique. First, it is very difficult to synchronize a local laser (also often referred to as a reference optical carrier or local oscillator) with the received modulated optical carrier in terms of phase and frequency because the optical frequencies are relatively large (typically, on the order of 200 THz). Second, it is very difficult to align the polarization of the local laser with that of the received optical signal because the polarization of the latter is affected by the optical transmission link and tends to change over time.